President Obama is expected to appeal to a cross section of Americans about the perils of rising temperatures and the economic benefits of dealing with climate change in a speech tomorrow that could establish a timeline for regulating carbon at existing power plants.

The effort at depoliticizing the thorny topic of climate began Saturday in a campaign-style video in which Obama pointed to different areas of the public that he said can help address the effects of warming. He identified scientists, farmers, engineers and workers as the beneficiaries of an economy that runs on cleaner fuels.

"And we'll need all of our citizens to do our part to preserve God's creation for future generations," Obama added. "There's no single step that can reverse the effects of climate change. But when it comes to the world we leave our children, we owe it to them to do what we can."

The speech, to be given at Georgetown University, is widely assumed to be an announcement including the administration's intent to regulate the amount of greenhouse gases that can be released by the nation's electricity sector. It's unclear how quickly those rules would be drafted, or how aggressively they might cut emissions.

Some analysts view the EPA rules as the strongest short-term step that the president can take on climate, with the electricity sector contributing about 40 percent of U.S. emissions. But it doesn't address the administration's longer-term goals of cutting emissions by 80 percent later this century.

"It's a landmark for climate policy," said Nathaniel Keohane, who worked in the White House when carbon regulations for new power plants were proposed over a year ago. "Ultimately, as the president himself has said, we need Congress to act -- but this is a significant step that the administration can take right now using the tools available."

Keohane, now a vice president with the Environmental Defense Fund, believes the announcement will paint a fuller portrait of Obama's governmentwide effort to tackle climbing temperatures, beyond the power plant rules. The plan could accelerate action within a host of agencies, like the Departments of Energy, Interior and Agriculture, on renewable power, energy efficiency and other policies, he said.

Doubts about timing
As a basis for those efforts, Obama could point to the increased threat of natural disasters, such as coastal flooding, droughts and wildfires. The 90-second video released Saturday shows footage of stormy coastlines, industrial smokestacks and melting snow fields.

The White House's sudden pivot to the climate issue has encouraged some environmental advocates but raised question marks with others.

"It's awfully good to see the president starting to move forward on climate action -- after the hottest year in American history, it's appropriate that the White House would move to act. And the solutions agenda they've begun to advance moves the country in a sane direction," said Bill McKibben, the head of 350.org.

He added: "Today's announcement also makes me think it's more likely the White House will reject the Keystone pipeline, which is the biggest environmental battle in a generation -- the president is a logical man, and taking two steps forward only to take two back would make no sense.

"The world desperately needs climate leadership, and today Barack Obama showed he might turn out to be the guy who provided it."

But other climate advocates are more skeptical about Obama's timing and overall intention. One said that the administration has already delayed the rules for both new and existing power plants, both of which have been promised by EPA. This advocate, who asked not to be named, believes the president is trying to please his base before approving, potentially, the Keystone XL pipeline, which is detested by many environmentalists.

The advocate is also concerned that Obama might not fulfill the promises he announces tomorrow.

"If I had to bet, I'd bet that this was good news and he'll follow through on this stuff. On the other hand, I wouldn't bet the farm on it," the advocate said. "If EPA were proposing existing power plant standards on Tuesday, that would be one thing. But that's certainly not going to happen. I wouldn't be surprised to see the proposal date, you know, in six months to a year, which means that the final would be during the presidential campaign season.

"So it's vulnerable to the same sorts of excuses that were used for not doing anything before."

The details of Obama's plan are unknown, but it is clear to many that the announcement marks the first big action on climate change since three years ago, when the Senate failed to approve a House-passed cap-and-trade bill.

Paul Bledsoe, who worked in the White House on climate issues under President Clinton, sees Obama's action as a sign of his personal concern about the impacts of rising carbon dioxide, which recently passed 400 parts per million, a measurement not seen on Earth for tens of thousands of years.

"It is also critical that the U.S. show leadership in cutting emissions if we are to compel other major emitters like China to do so," Bledsoe said. "Domestic and international climate action are both essential to address the problem."

In the video, Obama makes his case to the public without mentioning politics and the likelihood that climate policies will stoke partisan divisions. Instead, he bases his appeal on the idea that it's a threat facing the nation.

"So I hope you'll share this message with your friend, because this is a challenge that affects everyone," the president says. "And we all have a stake in solving it together."